1. Field of the Art
The present invention relates in general to a pneumatic control device for controlling a pneumatic system such as a pneumatic circuit for operating an air-conditioning system for an automotive vehicle, and more particularly to such a pneumatic control device including a plurality of changeover switches which are controlled by selectively depressing a plurality of push levers, so as to place the pneumatic system selectively in a plurality of operation modes corresponding to the push levers. The invention is also concerned with the construction of the changeover switches.
2. Related Art Statement
In an air-conditioning or air-controlling system of an automotive vehicle, an air damper is generally disposed in an air passage for conditioning the air in the room of the vehicle. The damper is operable in different positions to place the air-conditioning system selectively in one of a plurality of operation modes. Recently, such a damper is operated by a pneumatically-operated member such a diaphragm which is operated by a vacuum air source easily available on the automotive vehicle. The use of a vacuum air source for operating the diaphragm leads to constructional simplification of the control device for controlling the air-conditioning system. Further, the vacuum-operated control device meets the recent taste of the vehicle operators. More specifically, changeover switches are connected between the vacuum source and the vacuum-operated diaphragm to control the fluid communication between the vacuum source and the diaphragm, while push levers corresponding to the operation modes of the air-conditioning system are provided to control the operations of the changeover switches, in order to place the air-conditioning system in the operation mode corresponding to the operated push lever.
For example, Japanese Utility Model Application laid open under Publication No. 50-33442, shows such a pneumatic control device which uses vacuum control switches of piston type wherein a piston is movable in a cylinder to control fluid communication between the vacuum source and a vacuum-operated actuator for controlling the air-conditioning system. An alternative control device is known according to Japanese Utility Model Application published for opposition purpose under Publication No. 56-4489. This latter control device uses changeover switches of micro-switch type which are operated by depression of their pushbuttons, to control air passages for the air-conditioning system.
In the former pneumatic control device using the piston type control switches, the piston connected to a push lever is biased by a spring in a direction that causes the piston to project out of the cylinder. When the operation mode of the air-conditioning system is changed, the push lever must be operated against a biasing force of the spring for the piston, as well as a biasing force of a return spring which is provided for returning the operated push lever to its non-operated position. Thus, the control device inevitably requires a relataively large force to operate the push lever.
In the latter pneumatic control device using the micro-switch type changeover switches, too, a biasing spring is disposed in each switch such that the biasing force increases the required operating force that must be applied to the corresponding push lever, as in the control device using the changeover switches of the piston type indicated above.
In the above latter control device, a plurality of plate cams are disposed in mutually spaced-apart relation to actuate the pushbuttons of the corresponding changeover switches. The push levers are held in their operated positions by corresponding lock plates. These plate cams and lock plates are biased by respective springs in the predetermined directions. To operate each changeover switch, the push lever must be moved against the biasing force of the corresponding plate cam and the biasing force of the corresponding lock plate. Thus, the use of these additional springs further increase the required force for moving the push levers to their operated position. Further, the spaced-apart arrangement of the plate cams and the lock plates results in increasing the overall size of the pneumatic control device. This is not desirable since the control device is generally installed on an isntrument panel of the vehicle, whose space for the control device is relatively limited.